Coenzyme Q10 (also known as CoQ10, Q10, vitamin Q10, ubiquinone, and ubidecarenone) is a benzoquinone compound synthesized naturally by the human body. The "Q" and the "10" in the name refer to the quinone chemical group and the 10 isoprenyl chemical subunits, respectively, that are part of this compound's structure. The term "coenzyme" denotes it as an organic (contains carbon atoms), nonprotein molecule necessary for the proper functioning of its protein partner (an enzyme or an enzyme complex). Coenzyme Q10 is used by cells of the body in a process known variously as aerobic respiration, aerobic metabolism, oxidative metabolism, or cell respiration. Through this process, energy for cell growth and maintenance is created inside cells in compartments called mitochondria. Reviewed in [1,2,3,4] Coenzyme Q10 is also used by the body as an endogenous antioxidant. Reviewed in [1,2,4,5,6,7,8] An antioxidant is a substance that protects cells from free radicals, which are highly reactive chemicals, often containing oxygen atoms, capable of damaging important cellular components such as DNA and lipids. In addition, the plasma level of coenzyme Q10 has been used in studies as a measure of oxidative stress (a situation in which normal antioxidant levels are reduced).[9,10]
Coenzyme Q10 is present in most tissues, but the highest concentrations are found in the heart, the liver, the kidneys, and the pancreas. The lowest concentration is found in the lungs. Tissue levels of this compound decrease as people age, due to increased requirements, decreased production, or insufficient intake of the chemical precursors needed for synthesis. Reviewed in  In humans, normal blood levels of coenzyme Q10 have been defined variably, with reported normal values ranging from 0.30 to 3.84 µg /mL.[13,14] Reviewed in [2,4]
Coenzyme Q 10 is a compound that is made naturally in the body. The body uses it for cell growth and to protect cells from damage that could lead to cancer (see Question 1).
Animal studies have shown that coenzyme Q10 helps the immune system work better and makes the body better able to resist certain infections and types of cancer (see Question 5).
Clinical trials have shown that coenzyme Q10 helps protect the heart from the damaging side effects of doxorubicin, a drug used to treat cancer...
Given the importance of coenzyme Q10 in optimizing cellular energy production, use of this compound as a treatment for diseases other than cancer has been explored. Most of these investigations have focused on coenzyme Q10 as a treatment for cardiovascular disease. Reviewed in [2,4] In patients with cancer, coenzyme Q10 has been shown to protect the heart from anthracycline -induced cardiotoxicity (anthracyclines are a family of chemotherapydrugs, including doxorubicin, that have the potential to damage the heart)[3,16,17,18] and to stimulate the immune system. Reviewed in  Stimulation of the immune system by this compound has also been observed in animal studies and in humans without cancer.[21,22,23,24,25,26,27] In part because of its immunostimulatory potential, coenzyme Q10 has been used as an adjuvant therapy in patients with various types of cancer.[17,28,29,30] Reviewed in [20,31,32,33]